Researchers have found that important information is missing from many trials recorded on the international register of clinical trials ClinicalTrials.gov, a publicly accessible database of clinical trials managed by the US National Library of Medicine.

Joseph Ross, assistant professor of geriatrics at the Mount Sinai School of Medicine, New York, and colleagues sampled a cross section of trials on the registry. After excluding phase I safety trials, they identified 7515 trials that were registered within ClinicalTrials.gov after 31 December 1999 and whose record indicated trial completion by 8 June 2007.

All of the trials reported the essential information required by the registry, but optional data including the primary outcome of …